feat(dao): dao_discover_scripts MCP tool + Koios discovery client

New `aldabra-dao::discovery` module:
- `DiscoveryClient` trait + `KoiosDiscoveryClient` impl
- `discover_scripts(cfg, client, deployers)` — auto-finds:
  - governor_validator_ref + stake_validator_ref via deployer ref-script search
  - stake_st_policy from any existing stake UTxO (gov-token + non-gov-token asset)
  - stake_st_policy_ref via deployer search
- `apply_discovery(cfg, report)` — merges into DaoConfig (never overwrites)
- `script_hash_from_addr(bech32)` — extract 28-byte script hash from a script address

New MCP tool:
- `dao_discover_scripts { dao?, extra_deployers? }` — runs the audit logic
  against any registered DAO + persists the discovered fields back to the
  DaoConfig. Returns JSON with what was found + a gaps list for things
  v1 can't auto-discover (proposal_addr, proposal_st_policy).

Plus 4 unit tests with stub Koios responses validating the full pipeline:
script-hash extraction, StakeST discovery from stake UTxO assets,
validator ref-utxo matching at deployer, apply_discovery merge semantics.

WalletInner now caches `koios_base` so the discovery client can be
constructed on demand without re-passing the URL through args.

crates/aldabra-dao/src/lib.rs

@@ -28,6 +28,7 @@
 pub mod agora;
 pub mod builder;
 pub mod config;
+pub mod discovery;
 pub mod error;
 pub mod reader;